1. Field of the Invention
The present invention relates to internal combustion engines, and, more specifically, to an exhaust gas recirculation (EGR) system for such engines.
2. Description of the Related Art
In an ever increasing effort that began more than 30 years ago, systems have been provided for internal combustion engines to recirculate a portion of the exhaust gas in order to reduce the combustion temperatures and, in turn, reduce the generation of oxides of nitrogen or NOx. Initial developments were undertaken for spark ignition engines but subsequent research has caused this technique to be applied to compression ignition, or diesel engines. In an effort to increase the density of the EGR gasses, and thus the impact on efficiency, cooled EGR has been proposed. Such a system enables a greater quantity of recirculated products of combustion without adversely affecting performance. However, systems of this type have problems, among those being the lowering of the EGR gas to the point moisture in the air condenses thus forming water particles. These water particles combine with the components in the combustion gasses to produce various acids that have an adverse effect on materials used for heat exchanges and air carrying conduits, as well as combustion chamber components.
In an effort to provide even greater quantities of EGR, additional coolers have been proposed to increase the gas density even more to minimize the effect on combustion efficiency. The additional cooling process, while providing a benefit, carries with it the occurrence of additional condensation and generation of water particles. It has been proposed in various systems to bypass the secondary cooling function during conditions when generation of water particles would occur to avoid the adverse problem of water ingestion in uncontrolled amounts into the combustion cylinders. However, these systems fail to address the problem of moisture that has collected in the heat exchangers.
Therefore, what is needed in the art is an EGR system in which the moisture in heat exchangers for such systems is effectively purged without adverse impact on the engine.